1. Field of the Invention
The present invention generally relates to the detection of flaws in finished circular tablets which may be coated or uncoated. Particularly, it is concerned with a method for discriminating defective tablets from normal (non-defective) ones to discard or to process again the former ones, and an apparatus used for performing said method. It therefore enables the classification of the finished tablets during their travel along a transferring path bridging various equipment in a tablet processing line which may include a tabletting press, a coating pan, a polishing machine and a wrapping machine.
Finished tablets may occasionally be broken or specked by possible collision with respect to other tablets or other parts or components of any equipment during their transferring operations to any subsequent processing step, for instance, the coating or wrapping step. These flaws occur particularly on the circular edge lines of the tablets and the modes thereof may generally be classified into the following two modes according to the degree or the magnitude of the flaws.
These are elucidated in FIG. 1 of the drawings; one shown in FIG. 1A, wherein the plane shape of the tablet, i.e., the shape projected onto a plane vertical to the direction of pressing operation of the tablet, is no longer a circle with a broken part or parts, is referred to as a broken one, and that shown in FIG. 1B, wherein the body of the tablet is partly broken but its plane shape still remains a complete circle, is referred to as a specked one throughout this specification and claims. It is to be noted herein that a tablet having an elliptical section (for instance, a sugar-coated tablet) shown in FIG. 1C, is apt to be injured at its tapered but rounded circumferential edge, and the modes thereof may likewise be classified.
Such flaws may occur by various other causes in the tablet processing line and the frequency of their occurence is extremely low, i.e., in the order of from one five hundred thousandth (1/500,000) to one two million and five hundred thousandth (1/2,500,000). Although the frequency is extremely low, these defective tablets must imperatively be removed from the bulky lot of tablets, before they enter the subsequent steps, for example, a wrapping step, and therefore an operation for detecting such broken or specked tablets to classify and discriminate them from the normal ones must be interposed between the preceding step and the subsequent step.
2. Description of the Prior Art
Hithertofore, this operation has been performed by a mechanical method of introducing the tablet to be inspected into a vibrating sieve composed of a punched metal screen having perforations of a diameter of corresponding magnitude and by removing away the defective tablets through the perforations, and/or a non-mechanical method of visual inspection with human eyes of a plurality of inspectors.
According to the former method, i.e., the screening method, this itself is defective because broken or specked tablets cannot occasionally pass through the perforations of the sieve or screen but remain thereon, if a plane breadth of such tablet still remains identical to that of the normal tablet. In other words, if such tablets have a plane breadth larger than one second (1/2) of that of the normal one (all specked tablets have a plane breadth larger than one second (1/2) of that of the normal ones as defined above), the broken or specked tablets may often be transferred to any subsequent steps together with the normal ones without being removed.
The latter method, i.e., visual inspection by human's eyes, is also very difficult to perform properly, because the number of the tablets transferred through a tablet processing line, usually by a belt-conveyer, exceeds a rate of 1000-3000 tablets per minute and the inspecting operation must extend to very small specks. Furthermore, this method has another disadvantage in that it can only be performed properly on either side of the tablet at one time and enough inspection cannot be performed on the other side. Moreover, errors due to fatigue of the eyes of the inspector must not be disregarded.